On the question of the "fine correction" table, there may actually be four of them, one for each cylinder. Since the ECU, when it detects knock, can identify which cylinder caused it, it might want to maintain a separate ignition advance for each cylinder. However, there's an interesting FHI patent on knock control for the case where there is insufficient memory to store a separate table for each cylinder. It's US patent 4,726,339
and its main ideas are:
- identify which cylinder is most likely to knock and mount a knock sensor close to its combustion chamber
- only pay attention to that cylinder's knock
- adjust timing advance to control knock in that one cylinder
- apply that same timing advance to the other cylinders
Since the EJ20's knock sensor is obviously mounted closest to Cyl #4's combustion chamber, could that mean that Cyl #4 is ...